Karen is on the crosscountry team at her college While shes

Karen is on the cross-country team at her college. While she\'s running, her heart rate reaches 160 beats per minute (bpm) and her cardiac output reaches 27 liters/min but at rest her heart rate is only 65 bpm and cardiac output is 5 liters/min. Show equations and calculations. a) What is Karen\'s stroke volume at rest? b) What is Karen\'s stroke volume during exercise? c) According to the Frank-Starling Law of the Heart, is the End Diastolic Volume (EDV) or End Systolic Volume (ESV) directly related to the change in SV with exercise? Why?

Solution

Stroke volume is defined as the volume of blood pumped from the left ventricle per beat. Stroke\'s volume can be calculated by dividing the cardiac output with Heart rate.

SV = Q / HR

Where, Q = Cardiac output

HR= Heart Rate

1. Stroke\'s volume at rest = Cardiac output (at rest) / Heart rate( at rest)

= 5 (l/min) / 65 bpm

= 0.076 l (at rest)

2. Stroke\'s volume during exercise: Stroke\'s volume increases during exercise because the body demands for more oxygen filled blood.

Stroke\'s volume (exercise)= Cardiac output (exercise) / Heart rate (exercise)

= 27 / 160

= 0.168 l (During exercise)

3. The End-diastolic volume (EDV), or End-systolic volume( ESV) are related to Stroke\'s volume(SV) as follows:

SV= EDV-ESV

Prolonged aerobic exercise training may also increase stroke\'s volume, which results in lower heart rate. Reduced heart rate prolongs ventricular diastole, increasing end-diastolic volume and ultimately allowing more blood to be ejected.